cyclones and anticyclones, ridges and...
TRANSCRIPT
![Page 1: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/1.jpg)
Cyclones and Anticyclones, Ridges and Troughs
Schematic surface map showing a cyclone / anticyclone pair
● Isobars on surface maps often have a closed appearance (as illustrated)
● Areas of low pressure are called cyclones, while areas with high pressure are called anticyclones
E
N
H
L
low pressure area / cyclone: cloudy or rainy weatherhigh pressure area / anticyclone: fair weather
● Rule of thumb:
1014
998
![Page 2: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/2.jpg)
Example surface plot from last spring, showing closed contours around highs and lows
![Page 3: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/3.jpg)
Surface isobars and cloud cover (yellow) for the same case, showing cloudy conditions over the low pressure area
![Page 4: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/4.jpg)
Radar image showing areas of rain (green) and snow (pinkish) associated with the low pressure system
![Page 5: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/5.jpg)
heights of the 500 mb surface (km)
● On upper-level charts, height contours often have a wave-like appearance
- The part of the wave with higher heights is called a ridge, while the part with lower heights is called a trough
E
N
5.55.45.3
5.6
![Page 6: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/6.jpg)
E
N
L
trough ridge
5.55.45.3
5.6
heights of the 500 mb surface (km)
● On upper-level charts, height contours often have a wave-like appearance
- The part of the wave with higher heights is called a ridge, while the part with lower heights is called a trough
![Page 7: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/7.jpg)
Height contours for the 200 mb pressure surface for the same case as before, showing a wave pattern over the US
![Page 8: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/8.jpg)
Cyclones and anticyclones on a surface map
Ridges and troughs on an upper-level chart
![Page 9: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/9.jpg)
Temperatures and Pressure-Surface Heights
As a rule, warmer temperatures in the lower troposphere imply higher pressure surface heights at upper levels (e.g., at 500 mb). Why?
![Page 10: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/10.jpg)
Temperatures and Pressure-Surface Heights
As a rule, warmer temperatures in the lower troposphere imply higher pressure surface heights at upper levels (e.g., at 500 mb). Why?
● Well, for the sake of argument, suppose the pressure at the ground is nearly uniform, with value 1000 mb (roughly true)
![Page 11: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/11.jpg)
Temperatures and Pressure-Surface Heights
As a rule, warmer temperatures in the lower troposphere imply higher pressure surface heights at upper levels (e.g., at 500 mb). Why?
● Well, for the sake of argument, suppose the pressure at the ground is nearly uniform, with value 1000 mb (roughly true)
● Now recall that between any two given pressure levels, the mass of air between the two levels is always the same
- To be concrete, we'll pick 1000 mb and 500 mb
![Page 12: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/12.jpg)
Temperatures and Pressure-Surface Heights
As a rule, warmer temperatures in the lower troposphere imply higher pressure surface heights at upper levels (e.g., at 500 mb). Why?
● Well, for the sake of argument, suppose the pressure at the ground is nearly uniform, with value 1000 mb (roughly true)
● Now recall that between any two given pressure levels, the mass of air between the two levels is always the same
- To be concrete, we'll pick 1000 mb and 500 mb
● If the air is warm, then this mass of air expands, taking up more space. And if it's cold, it contracts, taking up less space.
![Page 13: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/13.jpg)
warmcold
column of air expands
column of air contracts
● If the air is warm, then the mass of air expands. And if the air is cold, then it contracts.
● This expansion of the column where it's warm means that the pressure surfaces at upper-levels will have higher heights. And vice-versa where it's cold.
500 mb surface
![Page 14: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/14.jpg)
warmcold
column of air expands
column of air contracts
● If the air is warm, then the mass of air expands. And if the air is cold, then it contracts.
● This expansion of the column where it's warm means that the pressure surfaces at upper-levels will have higher heights. And vice-versa where it's cold.
● One consequence is that in general, pressure surfaces slope downwards from equator to pole
500 mb surface
![Page 15: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/15.jpg)
![Page 16: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/16.jpg)
Same 200 mb surface as before, showing heights decreasing towards the pole
11.2 km contour
12.2 km contour
![Page 17: Cyclones and Anticyclones, Ridges and Troughspeople.tamu.edu/~cepi/atmo201/alt/ref/chap7_notes_b.pdfwarm cold column of air expands column of air contracts If the air is warm, then](https://reader035.vdocument.in/reader035/viewer/2022081601/611b8f26110ccf17726212dd/html5/thumbnails/17.jpg)
High to low, look out below! Planes flying with pressure altimeters have to be careful when flying into cold air.